The present invention is related in general to the development of polymeric solid hosts for use in laser-pumped, flashlamp-pumped and explosive shock-compressed argon/xenon plasma-pumped lasers which use fluorescent dyes as the gain medium, and more particularly to a formulation and preparative procedure for producing polymeric laser rods having a high enough concentration of fluorescent dye and sufficient optical quality to provide a gain medium for efficient laser oscillation.
The use of polymers as a host matrix for laser-pumped dye lasers (see, e.g., B. H. Soffer et al., "Continuously Tunable, Narrow-Band Organic Dye Lasers," Appl. Phys. Lett. 10(10), 266 (1967)) and flashlamp-pumped dye lasers (see, e.g., O. G. Peterson et al., "Stimulated Emission from Flashlamp-Excited Organic Dyes in Poly(methylmethacrylate)," Appl. Phys. Lett. 12(7), 238 (1968)) has been frequently investigated on an international level since those early reports (see, e.g., R. M. O'Connell et al., "Plastics for High-Power Laser Applications: A Review," Opt. Eng. 22(4), 393 (1983)). The majority of the literature and patents pertaining to this subject have been concerned with polymer hosts composed of poly(styrene) or modified poly(methyl methacrylate).
Modifications include the addition of solvents, comonomers, and low molecular weight plasticizers to impart both solubility of the dye and optical quality to the resulting matrix. There are numerous reports of polymer elements which are composed of poly(methyl methacrylate) incorporating copolymer additives such as methacrylic acid and hydroxyethyl methacrylate, or plasticizers such as ethanol, propanol, and dibutyl phthalate.
Specifically, for rhodamine-6G impregnated poly(methyl methacrylate) elements which were pumped with a doubled Nd:YAG (532 nm), conversion efficiency of up to 47% was reported for laser light at 562 nm (see, e.g., H. H. L. Wang et al., "A Simple, Efficient Plastic Dye Laser," Optics Comm. 18(4), 444 (1976)). In another report describing pumping with a doubled Nd:glass laser (530 nm), conversion efficiency of up to 46% was achieved using a formulation with 10% ethanol/methyl methacrylate polymer (see, e.g., D. A. Gromov et al., "Efficient Plastic-Host Dye Lasers," J. Opt. Soc. Am.:B 2(7), 1028 (1985)).
Furthermore, coaxial flashlamp-pumped lasing of 1.1.times.10.sup.-4 molar rhodamine-6G incorporated into a poly(hydroxyethyl methacrylate-co-methyl methacrylate) rod (0.95 cm D .times.18 cm L) was reported to have an output energy of 50 mJ with an electrical input to the lamp of 60 J. The single point efficiency was then 0.083% with a calculated energy/rod length of 2.8 mJ/cm. A 42 cm rod with 1.4.times.10.sup.-4 molar coumarin-540 in poly(methyl methacrylate) also had an output energy of 50 mJ with an input of 360 J to the lamp. The efficiency was 0.014% (1.25 mJ/cm) (see, e.g., D. P. Pacheco et al., "A Solid State Flashlamp-Pumped Dye Laser Employing Polymer Hosts," Proceedings of the International Conference on Lasers '87, F. J. Duarte, Ed. (STS Press, McLean Virginia (1988))). The rods were prepared in bulk and had relatively poor optical quality, as the researchers had to use a refractive index matching fluid and lenses within the oscillator cavity to obtain lasing. In Y. Hyosu et al., "Fluorescent Colored Resin Particles and Process for Preparation Thereof," U.S. Pat. No. 4,016,133, issued Apr. 5, 1977, a method is described for the preparation of fluorescent, colored resin (polymer) particles with excellent fluorescence, homogenous incorporation of the dye(s), and good lightfastness. A preferred formulation and aqueous emulsion polymerization process was used to make a fluorescent paint which could be applied to clothing. The preferred monomers and weight % composition were: ##STR1##
Examples of water-soluble fluorescent dyes included a few which are known laser dyes. This description was included to show a formulation which is similar to that of the present invention but would have to be further processed to make optical polymers suitable for lasing. Processing at elevated temperatures (&gt;100.degree. C.) would thermally destroy the heat sensitive dyes used for laser applications. Therefore, this would not be a useful method.
In S. J. Sheldrake et al., "Dye Impregnated Plastics for Laser Applications," U.S. Pat. No. 4,139,342, issued Feb. 13, 1979, a process for making dye-impregnated plastics for laser applications was described. A solvent-assisted process for nonuniform incorporation of laser dyes into poly(methyl methacrylate) over a period of 2-3 weeks with temperatures up to 95.degree. C. was employed. Using a doubled Nd:YAG laser, a conversion efficiency of 47% was achieved with a 1/8 in. sheet of active element containing nonuniformly mixed rhodamine-6G at a concentration of 1.0.times.10.sup.-4 molar. A disadvantage of the method disclosed by Sheldrake et al. is the lack of uniformity of the dyed plastic.
Accordingly, it is an object of the present invention to provide a copolymer composition which will permit homogeneous distribution of a laser dye (for a comprehensive listing, see, e.g., Laser Dye Catalog, Exciton Chemical Company, Inc., Dayton, Ohio (1989)) into a solid polymeric matrix at sufficient concentrations for significant output of lasing energy, using laser-pumped, flashlamp-pumped, and explosive shock-compressed argon/xenon excitation systems (see, e.g., Dye Lasers, F. P. Schafer, Ed., 2nd edition, Springer-Verlag, N.Y., pp. 83-84 (1977)).
Another object of the invention is to provide a process for the mass production of high optical quality plastics in the shape of disks or rods, suitable for use as gain media.
Yet another object of the invention is to provide a solid-state gain medium capable of lasing in the visible region of the electromagnetic spectrum (400-750 nm) using suitable fluorescent dyes and laser, flashlamp, or argon/xenon "bomb" pump energy.
Still another object of the invention is to provide a polymerizable laser dye which is incorporated into the polymeric chain at the molecular level and as a result is nonleachable.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.